The Posion Sky

Synopsis
The Valiant clears the ATMOS gas as the Sontarans activate their master plan to turn Earth into their cloning planet. UNIT is left defenceless, with a traitor in their ranks. And as interplanetary war edges closer, the Doctor has to fight to keep both Martha and Donna alive - but will he have to make the ultimate sacrifice?

Cast
The Doctor – David Tennant
Donna Noble – Catherine Tate
Martha Jones – Freema Agyeman
Rose Tyler – Billie Piper
Wilfred Mott - Bernard Cribbins
Sylvia Noble - Jacqueline King
Luke Rattigan - Ryan Sampson
Colonel Mace - Rupert Holliday Evans
General Staal - Christopher Ryan
Commander Skorr - Dan Starkey
Private Harris - Clive Standen
Private Gray - Wesley Theobald
Ross Jenkins - Christian Cooke
Female Student - Meryl Fernandes
Male Student - Leeshon Alexander
Captain Price - Bridget Hodson
Herself - Kirsty Wark
US Newsreader - Lachele Carl

Sontarans created by Robert Holmes